1. Field of the Invention
The present invention relates to tip guards for retractable writing instruments, particularly retractable marking pens.
2. Description of the Prior Art
Marking pens are presently in common use. These marking instruments commonly employ a tip (nib) in contact with a reservoir of ink contained in an ink cartridge placed within the instrument. These marking pens are often referred to as "felt tip" markers but in actuality the marking tip, i.e., the nib, is typically of plastic, felt or fiber, e.g., nylon, polyester or acrylic fiber. Such marking pens come with a tight-fitting cap to protect the ink absorbed in the marking tip from evaporating when the instrument is in non-use. Markers of this type are in common use and are readily obtainable in any stationery store.
There has been a long-standing desire to produce a marking pen having a retractable tip so that the marker pen may be placed in a shirt pocket without having to attach a protective cap. Although writing pens, such as ball point pens are commonly designed to be retractable, applicant is unaware of any retractable marking pens which are commercially available. Although several designs for retractable markers have been proposed in the prior art, these prior art designs have either proved to be too costly to manufacture for commercial acceptance or do not sufficiently prevent external material such as lint or fibers from contacting the marker tip when it is in retracted position and placed, for example, in a shirt pocket. Since the writing tip and barrel opening are small with ball point or fine tip writing pens, it has proved far easier to design an effective and economical retractable ball point or retractable fine tip pen than it has been to design an effective retractable marker.
In U.S. Pat. No. 3,583,820 a retractable writing pen is disclosed which includes a closure mechanism which protects the writing tip when the ink cartridge is in its retracted position. The writing tip is attached to the head of the ink cartridge. The writing instrument has a barrel and the ink cartridge is inserted in the barrel. The forward end of the barrel forms the writing end of the pen. A shield mechanism is located at the exposed end of the barrel. The shield has longitudinally extending fingers 18 which close upon themselves to shield the writing tip when the cartridge is in its retracted position. The extending fingers (18) which compose the head of the shield are held closed by an elastomeric band (24) which surrounds extending fingers (18). A circumferential recess (22) is provided around extending fingers (18) to receive the elastomeric band (24). As the cartridge 8 is pushed to the front of the barrel, the writing tip (40) penetrates the nose (20) of the shield and on retraction of the cartridge the nose portion (20) snaps tightly closed by the action of elastomeric band (24) around fingers (18). While the writing instrument disclosed in this reference is retractable, the barrel (4) which contains nose shield (20) is a separate element which must be separately attached to the end housing (60). Thus, the separate barrel assembly containing the shield mechanism described in this reference must be molded independently of the end housing (60) and therefore adds additional cost to the manufacture of the instrument. The shield mechanism described in this reference has the additional disadvantage that it is dependent on the elastomeric band to maintain a tight closure of the extending fingers (18) which comprises the shield. Elastomeric bands tend to stiffen with time and loose their elastomeric property, particularly when exposed to harsh environmental conditions or moisture. Additionally, the shield mechanism is intended to protect only small writing tips such as fine felt or fiber tip writing pens. The problem of protecting a larger tip head, as employed in marker pens, is far more difficult because the amount of exposed surface area of the marker tip is greater.
In U.S. Pat. No. 4,269,525 a shield mechanism is disclosed, which is intended to protect the tip of a retractable felt tip writing instrument. The shield mechanism (16), which is employed in this reference, is a small disk which is located at the head of the barrel of the writing instrument. The disk has a plurality of small slit openings (17) in the surface of the disk as shown in FIG. 4. As the felt tip (14) of the writing instrument is pushed forward, it penetrates the disk surface and pushes the individual slices of the disk surface outwardly to form an opening through which the felt tip passes. Upon retraction, the individual slices of the disk surface is intended to automatically retract to form a closed, flat surface. While the design described in this reference has the advantage of simplicity, it has a distinct disadvantage in that there are a number of slit openings in the surface of the disk. e.g., eight slit openings as shown in FIG. 4. As the felt tip 14 is pushed forward, it contacts disk shield (16) leaving residual ink on the shield. This is a disadvantage because ink tends to build up on disk shield (16) and may be transferred to lint or fabric if the pen is placed in a shirt pocket. Also, since the sliced surface of the disk shield contains so many individual slices, it is difficult to assure that each slice will return to its original position, that is its closed position, over long periods of time. Even with the best materials, the resiliency of each one of the individual slices comprising the disk surface will tend to diminish on opening and reclosure. Thus, it will not be long before the slits 17 will enlarge enough to allow external material such as lint or pocket fibers to contact the tip. This, of course, is unacceptable particularly if the writing tip is larger, for example, as in typical marker pens. Thus, while the disk shield described in this reference has the advantage of simplicity, it has a distinct disadvantage inherent in the design itself, namely that a disk surface must be sliced into a multitude of individual pieces which in turn provides less protection for the writing tip over time.
Accordingly, it is an object of the invention to provide a tip guard for retractable marking instruments and the like wherein the guard protects the marker tip from contact with lint, fabric threads and external materials when the instrument is placed in a shirt pocket or in storage. It is a related object of the invention to eliminate the need for a separate closure cap for the marking instrument.
It is an important object of the invention to provide a tip guard which is integrally molded as part of the marking instrument outer casing wherein the tip guard automatically closes over the marker tip upon retraction of the tip into the casing.
It is an object that the tip guard easily opens as the marker instrument is placed in the writing mode.
It is an important object that the tip guard exhibit properties of high resiliency and recovery to permit the guard to reclose tightly over the tip irrespective of the number of retractions and the length of time that the tip is left in the writing mode prior to retraction.
It is a further object that the tip guard, upon retraction of the marking tip, provide sufficient closure protection for the tip so that evaporation of ink therefrom is reduced when the marking instrument is in non use.